Influence Of The Different Cultivation Measures On The Growth Of Weedy Rice And Its Competition With Cultivated Rice

Weedy rice (Oryza sativa f. spontane) is a troublesome weed accompanying the cultivated rice that is found in rice-planting areas all over the world. Because of their highly competitive capacity, this weed can remarkably affect rice yields. Moreover, red weedy rice contamination reduces the commercial value of rice products because its influences on kernel whiteness and uniformity. Weedy rice has been recognized as a main weed causing yield loss in Southeast Asia, Latin America and Europe. The occurrence of weedy rice is not yet a problem in China, but with the gradual adoption of direct seeding for rice cultivation it would almost certainly become as serious a problem in China as in many other countries. And it has spread rapidly in these regions where direct seeding or related technologies are adopted and become gradually popular, accompanied by less weed management. In order to confirm whether the cultivation measures alteration was the main reason of the rise of quantity of weedy rice and provided a scientific basis for integrated control over weedy rice, we conducted emergence rates of 15 weedy rice populations at different soil and water depths, the influence of 3 densities of weedy rice on the growth of itself and cultivated rice under different cultivation measures and the impact of Dandong weedy rice population volunteer on the growth of cultivated rice. The results are as followed.The results of the influence of soil depths and water depths on emergence rate of weedy rice demonstrated that, for most weedy rice, the emergence rates were low at 3 cm soil depth under moisturing condition, but weedy rice didn't have nearly no emergency at 2cm soil depth under flooding condition. At both moisturing and flooding conditions, the emergence rates of all experimental weedy rice populations decreased with increasing soil depth. However, the response of different weedy rice populations to soil depths is not similar in neither moist nor flooding condition. The emergence rates of 3 populations (Tieling, Shenyang and Dandong) were above 50% at 3cm soil depth under moisturing conditions, which were higher than other experimental populations. The above results indicated that the soil depth may affect emergence of weedy rice. Therefore, deep-tillage should reduce the emergence rates of the populations of weedy rice which are susceptible to the changes of soil depths and thereby lower the harm to cultivated rice. Flooding reduced the emergence rates of weedy rice significantly; however, the influence of flooding on different weedy rice was different. Emergence rates of 4 populations (Jinhua, Taizhou, Xuzhou and Heilongjiang) decreased by less than 30%, while 7 populations (Wuhu, Shenyang, Yangzhou, Tieling, Dandong, Wuhan and Yiyang) demonstrated 40% reduction approximately. So the emergency rates of weedy rice may be reduced by keeping a certain depth of water before cultivated rice planting.The results of the impact of cultivation measures on the growth of weedy rice and cultivated rice showed that, weedy rice growing with transplanted cultivated rice, displayed relatively low seedling survival rates, short shoot heights, low numbers of tillers and effective panicles, short panicle, less shoot biomasses and seeds quantity. The cultivated rice were affected slightly by weedy rice in aspects of seedling survival rates, shoot heights, the lengths, widths and areas of flag leaves, shoot biomasses and yields. This indicated that the growth of weedy rice, whose quantity seed production was 19.78kg/667m2, was inhibited and cultivated rice yield was guaranteed (up to 233.11 kg/667m2) in the presence of weedy rice under transplanting. Although the emergence rate of weedy rice didn't affected significantly, the numbers of tillers and effective panicles, and shoot biomasses were inhibited significantly under dry direct seeding measure compared with water direct seeding measure. However, due to high weedy rice density, weedy rice competed with cultivated rice for space and nutrients. This caused the reduction of its areas of flag leaves, tillers and effective panicle numbers and shoot biomasses of cultivated rice significantly. And cultivated rice yield decreased 67.41 kg/667m2 under dry direct seeding compared to transplanting. The emergence rate of weedy rice was lower 9.14% under water direct seeding than dry direct seeding, however the growth of weedy rice did not be inhibited after emergence under water direct seeding. Therefore weedy rice occurred at a large amount, up to 81.29 kg/667m2. Because the seeding density was lower under water direct seeding than dry direct seeding, the yield of cultivated rice was lowered to 43.71 kg/667m2 under water direct seeding than dry direct seeding.The results of the impact of weedy rice densities on the growth of weedy rice and cultivated rice demonstrated that with the increasing of weedy rice density, dry shoot biomasses decreased and 50% heading was prolonged significantly, seedling ratios, shoot heights, the lengths, widths and areas of flag leaves, tillers and effective panicle numbers, dry shoot biomasses, panicle length, plump grain numbers per panicle, total grain numbers per panicle and 1000-grain weights did not affected remarkably. The cultivated rice was decreased gradually in many aspects, such as the widths of flag leaves, tiller numbers, effective panicle numbers, dry shoot biomasses, panicle lengths, total grain numbers per panicle,1000-grain weights and actual yields etc, with the increasing of weedy rice density. The growth of cultivated rice was also influenced by the rise of weedy rice density which not only decreased the seedling survival rates, the areas of flag leaves, tillers, effective panicle numbers and dry shoot biomasses of cultivated rice, but also affected the yield of cultivated rice. The seedling survival rates, the areas of flag leaves, tillers and effective panicle numbers, dry shoot biomasses, panicle lengths, plump grain numbers per panicle, total grain numbers per panicle,1000-grain weights and actual yield were lowered 6.81%, 4.07cm2,2.34 ind./plant,2.34 ind./plant,61.76g/(5 plants),2.88cm,52.83 grain,52.33 grain,1.43g,181.32 kg/667m2 respectively than CK under density III.The impact of weedy rice volunteers on the growth of cultivated rice under different cultivation measures demonstrated that the experimental weedy rice did survive the harsh winter safely and germinated under due environment in the forthcoming year. However, due to seeds mildewing and necrosis, gnawed by wild animals in winter, cleared away before planting cultivated rice and the application of subsequent cultivation measures, no volunteer seedlings occurred under transplanting, but the average seedlings per plot were 10.08 and 9.42 under water direct seeding and dry direct seeding respectively. Meanwhile, the cultivated rice yields wasn't affected significantly, up to 478 kg/667m2,453 kg/667m2 and 628 kg/667m2 under water direct seeding, dry direct seeding and transplanting. The above results showed that parts of experimental weedy rice survived over winter time and seeded, and then these seeds entered down to the field and could threat next year's rice yields.Considered all these results as a whole, transplanting was the best method against weedy rice in our experiment. This method could not only reduce the quantity of weedy rice, but also assure a good harvest of the cultivated rice. Though water direct seeding provided a better control over weedy rice seedling survival rates than dry direct seeding, it didn't affect the growth and the production of seeds after pollination of weedy rice. Due to the planting density of cultivated rice in water direct seeding was lower than that in dry direct seeding, the yield of cultivated rice in water direct seeding was similar to or lower than that in dry direct seeding. Although the yield of cultivated rice was higher under dry direct seedling than water direct seedling, weedy rice seedling survival rates was higher under dry direct seedling. This resulted in the occurrence of lodging and yield reduction. Therefore the rotation of direct seeding and transplanting should be adopted to control weedy rice. In order to balance payment, we should apply transplanting in high weedy rice occurrence farming field; water direct seeding in field of medium occurrence, dry direct seeding in low one. The cultivated rice seeding quantity should be increased in water direct seeding appropriately.